Cold hardiness & minimum temperature

Is Candle Larkspur 'Guardian Blue' (Delphinium elatum)cold hardy? Hardiness zone & min temp

Also called Candle Larkspur, Larkspur, Perennial Delphinium.

More about candle larkspur 'guardian blue'

About Candle Larkspur 'Guardian Blue'

Delphinium elatum · also called Candle Larkspur, Larkspur · flowering

A tall, stately perennial producing dense, upright spikes of clear blue flowers with white 'bee' centres in early to midsummer. 'Guardian Blue' is a reliable seed-raised cultivar suited to borders and cottage gardens. All parts of Delphinium are highly toxic to dogs, cats, horses, and humans, containing norditerpenoid alkaloids.

Cold limit: USDA 3-7 · RHS H7 (-20-25°C)

What candle larkspur 'guardian blue''s hardiness rating actually means

Yes — candle larkspur 'guardian blue' is genuinely cold hardy. Rated RHS H7 and USDA 3-7, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H7 means: Hardy in the severest European continental winters. On the US scale that maps to USDA 3-7 — the zones where it can be left outdoors year-round.

New to these scales? The USDA hardiness zone map explained covers how the zone numbers work, and you can find your own zone with the zone finder.

Minimum temperature — and what happens below it

Minimum survivable temperature is roughly below about −20 °C. Candle Larkspur 'Guardian Blue' is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for candle larkspur 'guardian blue' as it gets too cold:

It tolerates winter lows to about −20 °C once established.
Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root.
First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.

Can candle larkspur 'guardian blue' go outside or overwinter — and where?

Plant it out within USDA 3-7 and it overwinters with little or no help.
It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy.
The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

Work back from your local frost dates with the frost-date calculator: the last spring frost and first autumn frost are what really decide when candle larkspur 'guardian blue' can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Candle Larkspur 'Guardian Blue' hardiness — frequently asked questions

Is candle larkspur 'guardian blue' cold hardy?

Yes — candle larkspur 'guardian blue' is genuinely cold hardy. Rated RHS H7 and USDA 3-7, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Candle Larkspur 'Guardian Blue' is hardy across USDA 3-7; it belongs in the ground or a frost-proof container, not on a windowsill, and many types actively need a cold winter to perform.

What is the minimum temperature candle larkspur 'guardian blue' can survive?

Minimum survivable temperature is roughly below about −20 °C. Candle Larkspur 'Guardian Blue' is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is candle larkspur 'guardian blue'?

Candle Larkspur 'Guardian Blue' is rated USDA 3-7 and RHS H7 — Hardy in the severest European continental winters.

Can candle larkspur 'guardian blue' survive winter outside?

Plant it out within USDA 3-7 and it overwinters with little or no help. It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy. The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

What happens to candle larkspur 'guardian blue' below its minimum temperature?

It tolerates winter lows to about −20 °C once established. Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root. First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.